P0637Generic code

P0637 Code: Power Steering Control Circuit High

The P0637 code means the computer sees high voltage in the power steering control circuit, from an open circuit or a short to voltage. It can cause heavy steering or the loss of variable assist. Check the connector and wiring first.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$50 to $900
Difficulty
Medium
System
Chassis, Brakes and Suspension
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0637 code means

On some vehicles the computer controls a valve or a motor that adjusts the steering assist according to speed: more help when parking and less on the highway.

The computer watches the control circuit from its own driver transistor. The P0637 code flags high voltage in that control circuit, either an open circuit or a short to voltage. Before you replace the component, check the fuse, relay, connector and wiring, which are the most common causes.

If the circuit fails, the steering usually ends up with a fixed level of assist (heavy during maneuvers or too light on the highway). On electric power steering, the fault can switch the assist off, and the steering wheel becomes very heavy.

To confirm the fault, measure the continuity of each wire between the component connector and the computer connector with the key off. It should be under 1 ohm, and an infinite reading means the wire is open. If the wiring is good, measure the component itself: infinite resistance confirms it is open inside.

P0637 code symptoms

  • Check engine light or another warning light on.
  • Heavy steering, or no variable assist.
  • Steering is heavy when parking.
  • Steering is too light at high speed.
  • Steering warning light on.

Likely causes of the P0637 code

  1. Loose or broken connector. The most frequent cause, especially after another repair.
  2. Open coil or motor. Infinite resistance.
  3. Control wire cut between the component and the computer.
  4. Short to 12 volts. The control wire touches another wire that carries voltage.

How to diagnose the P0637 code step by step

  1. Activate the component with the scan tool and check whether it responds.
  2. Check the fuse and relay. Measure the voltage on both sides of the fuse, and swap the relay with an identical one.
  3. Measure the supply at the connector. You should see battery voltage with the key on or when the component is activated.
  4. Measure the resistance of the component and compare it with the manual. Also check the insulation to ground.
  5. Check the control wire for continuity to the computer and for shorts.

How to fix the P0637 code

  • Repair the connector, the wiring or the power supply.
  • Replace the power steering control if it does not respond even with correct power and command signals.
  • Clear the codes and verify the repair.

Technical reference data

  • The control valve is driven by a PWM signal, or it is an electric motor, depending on the system.
  • Reference values: check the manufacturer data for your vehicle.

Brand-specific notes

This code shows up on a few steering designs, so know which type your vehicle has before you start testing.

P0637 on GM

It appears on GM vehicles with variable assist steering.

P0637 on Electrohydraulic Steering

It also appears on some vehicles that have electrohydraulic power steering.

Frequently asked questions about P0637

Can I drive with a P0637 code?
With caution. Heavier steering takes more effort, especially when maneuvering, so be careful at low speed and when parking.
What does the power steering control do?
On some vehicles the computer controls a valve or a motor that adjusts the steering assist by speed. You get more help when parking and less on the highway.
Do I always have to replace the part?
No. Check the fuses, relays, connectors and wiring first, because they are the most common cause.
How much does it cost to fix P0637?
As a rough guide, between $50 and $900. A connector or wiring repair is at the low end, and replacing the control component is at the high end.
What does the P0637 code mean?
It is a generic OBD2 code that means the computer sees high voltage in the power steering control circuit, from an open circuit or a short to voltage.
What is the most common cause of P0637?
A loose or broken connector, especially after another repair was done nearby. A P0637 code can also come from an open coil or a cut control wire.

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